Incidence Density
A cohort study (hypothetical) was conducted to look at survival after experiencing a myocardial infarction (heart attack). Ten participants were followed for 3 years, resulting in the following table:
|
Follow-up Time (Months)
|
Event
|
|
3
|
Death
|
|
5
|
Censored
|
|
8
|
Death
|
|
12
|
Death
|
|
17
|
Censored
|
|
19
|
Censored
|
|
27
|
Death
|
|
32
|
Censored
|
|
36
|
Followed until end of study period
|
|
36
|
Followed until end of study period
|
1) What is the cumulative survival probability at the end of the follow-up period?
2) Using the same data, calculate the overall death rate per 100 person-years.
3) Calculate the rates separately for the 3 years of follow-up.
4) Is it appropriate to report an overall 3-year death rate for this study? Why or why not?
Attributable Risk
A hypothetical cohort study looked at the association between family history and the risk of developing Alzheimer's disease. The results were as follows:
|
|
Alzheimer's Disease
|
No Alzheimer's Disease
|
Totals
|
Incidence of AD
|
|
Family History
|
50
|
1,950
|
2,000
|
25 per 1,000
|
|
No Family History
|
25
|
2,975
|
3,000
|
8.3 per 1,000
|
|
Total
|
75
|
4925
|
5000
|
|
5) Calculate the attributable risk for Alzheimer's disease due to family history. Interpret the calculation in words.
6) Assume the prevalence of family history in the general population is 5%. Calculate the population attributable risk and interpret it in words.
Now assume the prevalence of family history in the general population is 25%. What effect does this change have on the estimate of the population attributable risk? Discuss the relationship between the population prevalence of exposure and the population attributable risk. Why is it important to understand this relationship as a public health professional?